Mark Smith
2017-07-13 05:18:16 UTC
On Wed, Jul 12, 2017 at 11:39 AM, Brian E Carpenter <
I would suggest that future protocols need to define what makes sense
for them, and mandating a constant in advance isn't necessary or even
appropriate.
for them, and mandating a constant in advance isn't necessary or even
appropriate.
architecture either not mentioning 64 at all, or *recommending* 64,
or requiring 64 "except if the first three bits
of the address are 000, or when the addresses are manually
configured, or by exceptions defined in standards track documents."
IMHO any of those three formulations would resolve Nick's problem
statement (given that there is also a citation of BCP198 in the
latest draft to clarify how routing works).
done and I think opposite to one of IPv6's major themes. Forming IIDs
should not be left to link-layer specific protocol specs.
I think one of the significant differences between IPv4 and IPv6 is
that a number of mechanisms have been made more generic and less
link-layer specific, or have been shifted from out of the link layer.
Specifically,
- ND is part of ICMP, rather than being a link-layer specific protocol
a ARP was.
- ND itself also tries to be as generic as possible, so that it can
operate over all link-types. Link unicast is a given, it expects a
link to emulate multicast if it isn't natively supported.
- IP and higher layer parameter configuration has been moved out of
PPP to upper layer and generic, non-link-layer specific protocols such
as RAs and DHCPv6.
We did have link-layer specific methods to generate IPv6 IIDs for
SLAAC, however RFC8064/RFC7217 has just deprecated all of them. IID
generation could be made link-layer agnostic because it was for
convenience rather than necessity.
Stateful DHCPv6 doesn't do link-layer specific or dependent addressing either.
Another way to consider what the IPv6 layer/protocol does is that it
abstracts away link-layer differences. As RFC6272 says in its overview
of the Internet Protocol Suite,
"The Internet layer provides a uniform network abstraction network
that hides the differences between various network technologies.
This is the layer that allows diverse networks such as Ethernet,
802.15.4, etc. to be combined into a uniform IP network. New network
technologies can be introduced into the IP Protocol Suite by defining
how IP is carried over those technologies, leaving the other layers
of the IPS and applications that use those protocol unchanged."
So, with IPv6 abstracting away the link-layer differences, for
consistency, IPv6 addresses are better to be abstract and decoupled
from underlying link-layer characteristics such as the link-layer
address characteristics and values.
Regards,
Mark.